Cretaceous-rocks-of-Tiruchinopoly in tamilnadu.pptx

A simplified presentation of Cretaceous rocks of thirichinopoly

1. Cretaceous Rocks of Tiruchirapalli The Cretaceous rocks of South India crop out in five main sectors, viz., Tiruchirapalli, Sivaganga, Vriddhachalam and Thanjavur in the Tamil Nadu and in the Union Territory of Pondicherry. All these outcrops are the parts of the Cretaceous successions of the Cauvery basin, South India. The Cauvery basin is a large basin with an approximate aerial extent of about 25,000 km2 and consisting of well preserved shallow marine Cretaceous sedimentary sequences of the Albian to Maastrichtian age, deposited along the eastern coast of the Tamil Nadu. Among these outcrops, the Cretaceous rocks are best developed in the Ariyalur area near the Tiruchirapalli sector. Here, the sequence represents one of the finest developments of the marine fossiliferous Cretaceous sequence in the world. The basin has yielded the rich and diversified assemblages of molluscs, brachiopods, cephalopods, echinoderms, corals, bryozoans, foraminifers, ostracods, algae and nanoplanktons, which have been extensively used to infer the age and depositional environment of the basin. Upper part of basin has yielded the fossils of freshwater and land vertebrates such as fish, dinosaurs, crocodiles, frogs and mammals. It may be noted that the marine transgressions invaded a large tract of the Coromandel Coast during the Cretaceous, which resulted the almost continuous shallow marine sedimentation from the Albian to Maastrichtian in the basin that continued upwards into the Lower Cenozoic, as well. However, some freshwater environment also prevailed during the sedimentation of the Upper Maastrichtian rocks in the basin. by Summa

2. Classification of Cretaceous Rocks Uttattur Group The Uttattur Group unconformably overlies upon the Archaean crystalline rocks. It attains a thickness of about 820 m and is subdivided into four formations namely, Terani, Arogyapurum, Dalmiapuram and Karai in chronological order (Table 6.4). The group as a whole is composed of fine silts, fossiliferous limestones, calcareous shales and sandy clays with phosphatic nodules, calcareous concretions and gypsum. At several places pale to pure and compact coral limestone is present at the base of the Uttattur sequence. Trichinopoly Group It unconformably overlies the Uttattur Group and is divided into two formations: Anaipadi and Kulakkalnattam (Table 6.4). It is composed of calcareous grit, sandstone and some shale and sandy clay with bands of shelly limestone, with gastropods and pelecypods, near the base. Granite pebbles commonly occur in the gravels and conglomerates. The beds contain abundant fossil wood, including huge tree trunks, false bedding and other features suggesting accumulation in shallow to coastal waters. A large number of invertebrates, especially pelecypods and gastropods with some cephalopods (Placenticeras andKossmaticeras), brachiopods, corals, marine reptiles, etc., occur within the Trichinopoly Group, but the assemblage is not as rich as that of the underlying Uttattur Group. The age of the group is from Turonian to Coniacian. The sediments of the group were deposited under a regressive shallow marine environmental condition. Ariyalur Group It is a poorly exposed and widely distributed group, lies unconformable above the Trichinopoly Group. It is subdivided into three formations: Sillakkudi, Kallankurichchi and Kallamedu in ascending order (Table 6.4). The group consists of sandstones with some marly clays, calcareous shales and limestones that display uniform bedding and very low dips. The lower part of the group has yielded well preserved remains of cephalopods (Karapaditesand Hauriceras), echinoderms, brachiopods, bryozoans, foraminifers, ostracods, etc. indicating a shallow, rather calm, marine environment of deposition of sediments. However, towards the upper part, it mainly yielded abundant remains of the terrestrialand freshwater vertebrates such as frogs, turtles, crocodiles and dinosaurs, suggesting a lacustrine environment of deposition.The Ariyalur Group is of Campanian to Maastrichtian age and unconformably overlains by the Niniyur Group of Paleocene age. Learners, you have learnt the Mesozoic succession of Rajasthan and Cretaceous of Tiruchirapalli. Now, spend few minutes to perform an exercise to check your progress.

3. Lithostratigraphy of Cretaceous Rocks Age Stage Group Formation Lithology Palaeocene ~~~~~~~~~~~~~~~~ Niniyur Group ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ Unconformity ~~~~~~~~~~~~~~~~~~~~~~ Campanian to Maastrichtian ~~~~~~~~~~~~~~~~~~~~~ Ariyalur Kallamedu Ferruginous arkosic sandstones, white to gray cross-bedded sandstones, calcareous sandstone, variegated clays, grit and fossiliferous limestones ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ Kallankurichchi Sillakkudi ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ Unconformity ~~~~~~~~~~~~~~~~~~~~~ Turonian to Coniacian Cretaceous Trichinopoly Kulakkalnattam Sandstones, limestones, siltstones and concretions of arenaceous limestones ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ Anaipadi ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ Unconformity ~~~~~~~~~~~~~~~~~~~~ Albian to Turonian ~~~~~~~~~~~~~~~~ Uttattur Karai Gypsiferous clays, sandstones, coral algal limestones, white, pink and yellow silty clay, kaolinitic clays, pebble conglomerates, phosphatic nodules and ferruginous sand interbeds ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ Dalmiapuram ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ Arogyapuram ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ Terani ~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ Unconformity ~~~~~~~~~~~~~~~~~~~~~~~~ Precambrian ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ crystalline basement ~~~~~~~~~~~~~~

4. Uttattur Group 1 Lithology The Uttattur Group is composed of fine silts, fossiliferous limestones, calcareous shales and sandy clays with phosphatic nodules, calcareous concretions and gypsum. At several places pale to pure and compact coral limestone is present at the base of the Uttattur sequence. 2 Fossil Evidence The lower part of group yielded plant fossils of Gondwanan affinities and deposited in the fluvial to deltaic environmental conditions.The upper part of the group is arenaceous, exhibits current bedding and yields abundant fossils comprising brachiopods, belemnites, bryozoans, corals, algae, bivalves, cephalopods (Eucalyoceras, Mammites and Lewesiceras), gastropods, foraminifers, calcareous sponges, sharks and marine reptiles and is considered to be deposited under shallow marine conditions. 3 Age The Albian to Turonian age has been assigned to the group based on fossils. 4 Depositional Environment The lower part of the group was deposited in fluvial to deltaic environments, while the upper part was deposited in shallow marine conditions.

5. Trichinopoly Group Lithology The Trichinopoly Group is composed of calcareous grit, sandstone and some shale and sandy clay with bands of shelly limestone, with gastropods and pelecypods, near the base. Granite pebbles commonly occur in the gravels and conglomerates. The beds contain abundant fossil wood, including huge tree trunks, false bedding and other features suggesting accumulation in shallow to coastal waters. Fossil Assemblage A large number of invertebrates, especially pelecypods and gastropods with some cephalopods (Placenticeras andKossmaticeras), brachiopods, corals, marine reptiles, etc., occur within the Trichinopoly Group, but the assemblage is not as rich as that of the underlying Uttattur Group. Age The age of the group is from Turonian to Coniacian. Depositional Environment The sediments of the group were deposited under a regressive shallow marine environmental condition.

6. Ariyalur Group 1 Lower Part The lower part of the group has yielded well preserved remains of cephalopods (Karapaditesand Hauriceras), echinoderms, brachiopods, bryozoans, foraminifers, ostracods, etc. indicating a shallow, rather calm, marine environment of deposition of sediments. 2 Upper Part However, towards the upper part, it mainly yielded abundant remains of the terrestrialand freshwater vertebrates such as frogs, turtles, crocodiles and dinosaurs, suggesting a lacustrine environment of deposition. 3 Age The Ariyalur Group is of Campanian to Maastrichtian age and unconformably overlains by the Niniyur Group of Paleocene age. Learners, you have learnt the Mesozoic succession of Rajasthan and Cretaceous of Tiruchirapalli. Now, spend few minutes to perform an exercise to check your progress.

7. Review Questions Question 1 List the name of the formations of the Mesozoic succession of Rajasthan in ascending order. Question 2 List the name of three groups of Cretaceous succession of Tiruchirapalli in ascending order. Question 3 Match the following: a. Ariyalur Group i. Lower Cretaceous b. Lathi Formation ii. Kallamedu Formation c. Habur Formation iii. Lower Jurassic

8. Triassic Succession of Spiti Group Age Series Beds Lithology Lilang Jurassic ---- Tagling limestone Massive limestones and dolomites ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ Megalodon limestone (Para Stage) Massive limestones and dolomites ~~~~~~~~~~~~~~~~ Triassic Tropites beds Dolomite limestones, shales and dark limestones with ammonite beds ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ Gray beds Gray shales and shaly limestone with pelecypod bed and an ammonite bed ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ Lower Dark shales and gray Muschelkalk limestones Nodular Hard nodular limestones limestone ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ Meekoceras zone Thin-bedded limestones and shales ~~~~~~~~~~~~~~~~ Lower Triassic ~~~~~~~~~~~~~~~~ Productus shale Dark shales ~~~~~~~~~~~~~~~~ Permian ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~

9. Summary of Mesozoic Era in India Marine Transgressions Mesozoic era in India is marked by extensive marine transgressions; which brought the marine sedimentation inside the continental areas. As a consequence, the Mesozoic successions are present both in peninsular and the Himalayan regions of India. Key Mesozoic Successions Triassic of Spiti, Mesozoic of Kachchh and Rajasthan and Cretaceous of Tiruchirapalli contain some of the best developed Mesozoic successions in India. Triassic Succession of Spiti Triassic succession of Spiti lies above the Productus shale of Permian age and below the Tagling limestone of Lower Jurassic age. Limestones, dolomites and shales are main lithology of the succession and it is divided into the Lower, Middle and Upper Triassic. Mesozoic Rocks of Kachchh The Mesozoic rocks of Kachchh contain a sequence of more than 2000m thick, ranging in age from the Middle Jurassic to the Lower Cretaceous. The sequence is divided into four formations: Pachcham, Chari, Katrol and Umia in an ascending order. Mesozoic Succession of Rajasthan Mesozoic succession of Rajasthan is well developed in the Jaisalmer region. It ranges in age from the Lower Jurassic to Lower Cretaceous and is divided into six formations: Lathi, Jaisalmer, Baisakhi, Bhadesar, Pariwar and Habur. Cretaceous Succession of Tiruchirapalli The Cretaceous succession of Tiruchirapalli is well developed in the Ariyalur area of the Cauvery basin. The age of sequence is Albian to Maastrichtian and is divided into three groups: Uttattur, Trichinopoly and Ariyalur in ascending order. Invertebrate Assemblages Invertebrate assemblages known from the Mesozoic rocks of Spiti, Kachchh, Jaisalmer and Ariyalur are found to be very useful in dating of these rocks successions. Deccan Traps The Mesozoic sedimentation was, however, terminated by the Upper Cretaceous, ending in the Deccan traps volcanic activity.

10. Conclusion The Mesozoic era in India was a period of significant geological activity, characterized by extensive marine transgressions and the deposition of diverse sedimentary sequences. These successions, found in both the peninsular and Himalayan regions, provide valuable insights into the Earth's history and the evolution of life forms. The study of these rocks, particularly the Triassic succession of Spiti, the Mesozoic rocks of Kachchh and Rajasthan, and the Cretaceous rocks of Tiruchirapalli, has yielded a wealth of information about the paleogeography, paleoclimate, and paleoecology of the Indian subcontinent during this era. The termination of Mesozoic sedimentation by the Deccan Traps volcanic activity marks a significant turning point in the geological history of India, paving the way for the formation of the unique landscape we see today.